I have a pinned Firefox (Nightly) shortcut in my icon task list applet. When I try to launch from the pinned area, the icon dims and flickers but firefox never loads. See this gif:

https://gfycat.com/DecentAnimatedHornbill

It still launches from the .desktop file in the main menu, and from the terminal without issues (no startup errors). All of my other pinned apps launch just fine, it's only Firefox.

@cybre I think you made that applet, figured I'd tag you just in case. Let me know if there is anything you'd like me to test.